Mining is the extraction of minerals or other geological materials from the earth from deposition such as an ore body, lode, vein, seam, reef or placer deposits. Ores recovered by mining can include, for example, metals, coal, oil shale, gemstones, limestone, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory. Mining can be accomplished via a variety of surface or subsurface techniques depending on the location of the deposit to be mined. Mining equipment has been developed for each different type of mining technique. For example, for performing subsurface mining techniques, a variety of below-ground drive prime movers such as, for example, continuous or drum miners, roadheaders, and rotary boring machines, have been developed.
Specifically with respect to potash, potash is a mineral that can be employed in many agricultural uses, such as fertilizers and animal feed. Potash can be found in mineral deposits, such as located in former lake-beds, and thus is often located in horizontal veins underground. Potash mining involves extracting the potash from these veins, often using room-and-pillar style mining and associated equipment, such as rotary boring mining machines. This type of mining, in which “rooms” are extracted from the mineral deposit while leaving “pillars” in between as supports, permits the extraction of a large portion of the vein.
Rotary boring mining machines are used in the underground potash mining to extract the concentrated KCl mineral in a sedimentary form. The mining machines cut the deposit materials, e.g. ore, by forcing rotary cutters into the mining face. For sake of simplicity, the mined or liberated material may be referred to as “ore,” but shall not be limited thereto. The liberated material is augured into the center of the machine by counter rotating rotors of the cutters and is conveyed through the middle of the mining machine to the rear by a chain conveyor. The chain conveyor dumps the liberated material onto an extensible conveyor which is operated behind the mining machine and consecutive conveyors delivery the material to a shaft where it is hoisted to the surface, such as by a skip, for further processing.
To maximize production, the extensible conveyor needs to be installed precisely behind the miner machine as mining progresses so the hardware of the system is perpendicular to the mining face and is centered on the conveyor line. This alignment ensures that the system operates effectively while minimizing spillage and damaging hardware due to the conveyor belt(s) running off-center and rubbing on the side of the hardware. The extensible conveyors are installed using a special bridge that is operably coupled to the mining machine with linkages and hydraulic cylinders, which provide four degrees of freedom to allow the bridge to be moved side-to-side and rotated left-or-right to ensure that the mining machine remains centered and aligned perpendicular to the mining face.
Furthermore, in order to extract the largest portion of the mineral deposits possible, it is preferable to maximize the ratio of room to pillar. Consequently, the use of extensible conveyors results in long rooms with narrow pillars between them. The placement of the pillars is also important in preventing loss of structural support to the mine. Thus, ideally, the pillars are made as narrow as possible between the rooms, while being precisely placed in order to provide sufficient structural support to ensure that the mine will not collapse. To accurately and precisely place pillars, rooms are often excavated using laser sight sensing devices. Otherwise, deviation from a straight bore would cause the pillar on one side of the room to become thicker, while decreasing the thickness of the pillar on the other side, potentially compromising the structural integrity of the mine overall. In conventional systems, such as rotary mining machine systems, the heading control consists of surveyors using theodolites to advance control spads. A pencil beam laser and rotary laser are positioned behind the spads so as to shine the laser light through plum bob strings suspended from the spads. The laser light projects a target on the front of the mining machine which the mining machine operators can observe and control the steering to maintain the laser on the target.
The laser sensing devices have been used as the target on the front of the mining machines which provides deviation information to the programmable logic controller (PLC). The PLC interprets the deviation data and provides steering control to automatically maintain the design heading. Although the extensible bridge motion is articulated from the mining machine, it gets the control information from the same laser that the mining machine uses. The laser strikes a pair of laser planes mounted on the bridge and the deviation information is translated into linear and rotational instructions that the bridge hydraulics execute. Continuous monitoring and corrective motion maintains the bridge and extensible conveyor in the proper alignment when installed and working properly.
However, using lasers and laser sensing elements for guidance has several limitations. The laser light loses strength the further it is away from the target, so as the mining machine cuts the face and advances, the operators have an increasingly difficult time seeing the laser light. Additionally, the sedimentary seam undulates and the mining machine is required to stay within a prescribed geological horizontal zone. As this horizontal zone undulates and the mining machine cuts higher or lower accordingly, the laser light strikes the roof or other structure or equipment which prevents the laser light from reaching the desired target on the front of the mining machine and bridge.
Advancing the survey line and lasers is time consuming and requires the mining machine to be shut down for approximately an hour or more while this work is done. Advancing the survey line is typically done by two groups of people: the surveyors and the miner operators. The surveyors use sophisticated surveying equipment that is very precise and ensures that the control spads are correctly and accurately aligned. The operators use the laser light that is several hundred feet back to install new control spads near the mining machine. This is less precise than using a survey instrument as the laser light is a quarter inch thick and is not perfectly aligned with the spads nearest to the lasers and so the error is multiplied when projected several hundred feet away. Occasionally there can be large deviations that require a heading correction, which results in conveyor alignment problems.
Conventional systems, using lasers and laser sensing elements such as detectors, have been used previously with limited success because the laser sensing element mounted on the front of the mining machine that was used for automated control loses sight of the laser very quickly as the mining machine is controlled up or down according to the undulating nature of the sedimentary ore body. The constant need to advance the survey line and laser equipment makes the conventional system undesirable.
As the mining equipment advances, pushing the face back into the potash vein for cutting, the conveyor system must be capable of following and remaining closely aligned with one another and with the mining equipment to prevent or inhibit the mined material from falling off the conveyor system, which could create inefficiencies, delays, or hazards. As the conveyor systems can reach several kilometers in length, slight misalignment can easily occur. Often, the locomotive force to advance the conveyor towards the face is provided via the mining equipment, and the conveyor and bridges must be capable of remaining sufficiently aligned with one another and with the mining equipment to operate reliantly and efficiently.
Furthermore, errors in laser alignment increase with distance from the source of the laser beam. Errors in laser beam angle result in increasing error in mining equipment positioning, proportional to the distance from the laser beam source. Errors in setup and alignment of the laser beam source made as the mining equipment is advanced can also compound one another to result in changes in heading, which can cause offset in angle or position along the conveyor system.
There remains a need for a more robust guidance system which reduces position errors and therefore increases mining efficiencies.